Thousand Guineas winner Commanding Jewel is an early defector from Saturday's Cockram Stakes at Caulfield.

Trainer Leon Corstens said he didn't think the mare was quite ready for this week's Group Three contest and was instead likely to head to a Listed race over 1000m at Moonee Valley on Saturday week.

Commanding Jewel, winner of three of her five starts, hasn't raced since taking out the Group One Thousand Guineas at Caulfield last spring and was an early nomination for the Cockram.

"She's not running. I don't think she's quite ready," Corstens said.

"If she happened to strike a heavy track it might bust her and we've got a long spring ahead. We'll take little steps."

Corstens, however, is delighted with the way Commanding Jewel is coming along heading to the spring carnival.

She is among nominations for the Cox Plate.

The mare, a three-quarter sister to unbeaten star Atlantic Jewel, looked good in a recent Moonee Valley exhibition gallop and also had a jump-out in wet conditions at Flemington last Friday.

"I'm really pleased with her," Corstens said.

"She's matured a hell of a lot."

Corstens is also conscious of Commanding Jewel's record and wants to have her in good shape when she does make her return.

Group One Oakleigh Plate winner Mrs Onassis was nominated for the Cockram Stakes on Sunday but trainer Gerald Ryan withdrew the mare's entry before nominations closed on Monday morning.

"I looked at the forecast for the rest of the week and there was rain coming later," Ryan said.

"I'm not going to risk her on a wet track. She doesn't handle it."

The Cockram Stakes has 24 nominations with the likes of last year's winner Lady Melksham and Australian Guineas runner-up You're So Good set to resume.

Group Two winner Oasis Bloom, who hasn't been seen since her dead-heat for fourth in last year's Group One Myer Classic, is also among the entries.